1. Field of the Invention
This invention involves optical fibers.
2. Description of the Prior Art
Optical fiber fabrication technology has advanced sufficiently far so that at the present time sophisticated engineering designs can be reduced to specific embodiments utilizing available fabrication processes. Both single mode and multimode fibers of very low loss are currently fabricated as a matter of course. In addition, mode dispersion in multimode fibers can be minimized by fabricating fibers with a radially graded index of refraction.
Despite the large strides that have been made in optical fiber fabrication technology, certain design parameters still remain unrealized because of limitations in either the fabrication process or the properties of the material used. One such area in which significant effort is still being applied involves the fabrication of optical fibers with high numerical aperture (N.A.). Such fibers require a core whose index of refraction is significantly greater than that of the cladding. However, materials with high enough index of refraction to be used in high N.A. fibers are most often found to have deleterious shortcomings in other areas; for example, they cannot be easily graded; they are hygroscopic; they melt at low temperatures; or they display high material dispersion.